If you've got three boards then you should get two of them repaired. One to run and one as a backup.
If you just buy an original running board it will eventually fail and you'll be back to where you are right now.
When you send one to a reputable person then they'll fix it right and bulletproof anything on the board that tends to fail.
Remember that even when you get one repaired that you may still have problems down the road. That thing was designed to run it a few years and it's now over 30 years old, so even though they fix the broken or parts known to fail then still have a board with a bunch 30+ year old parts on it. If you've got a backup board then you can swap them when one fails and send the broken one out for repairs.
There are several people here on KLOV that can fix them and Elektron Forge does a good job on the old Atari stuff. Look at the sticky for the who repairs what thread or find EF online.
-JM